Fix audio disconnect watch in connecting state

If disconnect_cb is not added until the connected state, the
callback will not be triggered if Device.Disconnected is called
while the audio profiles are still connecting.
diff --git a/audio/device.c b/audio/device.c
index 9554c7b..eff8231 100644
--- a/audio/device.c
+++ b/audio/device.c
@@ -231,7 +231,7 @@
 							priv->dc_id);
 			priv->dc_id = 0;
 		}
-	} else if (new_state == AUDIO_STATE_CONNECTED)
+	} else if (new_state == AUDIO_STATE_CONNECTING)
 		priv->dc_id = device_add_disconnect_watch(dev->btd_dev,
 						disconnect_cb, dev, NULL);